The Team Review Requests API just graduated from preview mode. It's now an official part of the GitHub REST API v3.
As outlined in this blog post we will be making a breaking change to the API. Going forward, when you GET/repos/:owner/:repo/pulls/:number/requested_reviewers it will return both users and teams in a hash syntax, instead of only users. Please take the time to update your API's accordingly.

Preview media type no longer needed

If you used the Team Review Requests API during the preview period, you needed to provide a custom media type in the Accept header:

application/vnd.github.thor-preview+json

Now that the preview period has ended, you no longer need to pass this custom media type.
Instead, we recommend that you specify v3 as the version in the Accept header:

application/vnd.github.v3+json

Please note, that GitHub Enterprise versions that do not yet support the Team Review Requests API will still require the custom media type.

Onward!
Thanks again to everyone that tried out the Team Review Requests API during the preview period.